In a typical application, the radio communications system might include as many as 100 different talkgroups, each containing 50 or so individual radio units e.g. mobile and/or hand-portable radios. The talkgroups may be of the `all informed` type in which data transmitted by each radio unit in a talkgroup will be received by all the other radio units in the same talkgroup.
The management of such a large number of talkgroups presents a significant technical problem. In one approach, a separate communications channel is assigned to each talkgroup. However, in practice, it is unlikely that the required number of channels would be available. Moreover, this approach would require excessive duplication of the system hardware.
In a preferred approach, the talkgroups share a relatively small number of channels. However, in existing systems, a finite set-up time is required in order to assign a communication channel to a talkgroup. More specifically, a radio unit must transmit, on a dedicated control channel, a request that one of the communication channels be assigned to its talkgroup. A finite set-up time is undesirable especially in the case of high priority communications for which delays must be kept to the minimum. Furthermore, the use of a dedicated control channel reduces the number of communication channels available to the talkgroups.
It is an object of this invention to provide a radio communications system which at least alleviates these shortcomings.